Collection! Comprehensive Guide to Energy Saving of Refrigeration Systems - Cold Storage System Edition

I. Energy-saving Control to be Noted for Energy Saving in Cold Storage
When the refrigeration system of a cold storage is in operation, while adjusting the energy-saving load of the compressor, the following aspects should be noted, for example:
(1) Under different working conditions and load conditions, reasonably match equipment such as compressors and air coolers to prevent energy loss caused by "using a large machine for a small task". Among them, the energy consumption of air coolers accounts for the largest proportion, approximately 23% to 38%. For example, take a 10,000-ton cold storage as an example. The storage rooms of this 10,000-ton cold storage are divided into 20 compartments, with a storage capacity of 500 tons in each compartment. Each compartment is equipped with 2 air coolers, and each air cooler is equipped with 3 axial fans with a power of 2.2 kW. There are a total of 120 axial fans in the whole cold storage. Since the air volume is directly proportional to the cooling capacity, and the fans are equipped according to the maximum cooling load. During the initial goods-in period, the cooling capacity is large, and all fans should be turned on. However, when the cooling and processing of the goods are basically completed and the temperature in the storage has stabilized, the number of axial fans turned on should be reduced in a timely manner. If calculated based on turning on 2 fewer axial fans in each storage room, 40 fans can be turned on less, with a total power of 88 kW, which is more than the energy consumption of 1 6AW-12.5 type compressor, and the energy saving can reach 25%. Moreover, turning on too many fans is likely to generate heat, increasing the cooling energy consumption of the system.
(2) Effective management of heat exchange equipment can also play an effective role in reducing energy consumption. Because when the evaporation temperature is -10°C, for every 1°C decrease in the condensing temperature, the power consumption per unit cooling capacity of the compressor decreases by 2.5% to 3.2%; when the condensing temperature is 30°C, for every 1°C increase in the evaporation temperature, the power consumption per unit of the compressor decreases by 3.1% to 3.9%. It can be seen that managing heat exchange equipment well is of great significance for reducing energy consumption.
(3) Measures to reduce energy consumption of heat exchange equipment:
① Drain the oil in a timely manner when there is too much oil: The thermal resistance of oil is much higher than that of metal, 20 times that of iron. An oil film adhering to the surface of the heat exchanger will cause the condensing temperature to rise and the evaporation temperature to drop, leading to an increase in energy consumption. When there is an oil film of 0.1mm adhering to the surface of the condenser, the cooling capacity of the refrigeration compressor drops by 16%, and the power consumption increases by 12.4%; when the oil film in the evaporator reaches 0.1mm, the evaporation temperature will drop by 2.5°C, and the power consumption will increase by 11%. At the same time, if the evaporation temperature is too low, the oil sludge is not easy to be carried back to the low-pressure circulation drum after entering the evaporator, and it is likely to cause the blockage of the evaporator. Therefore, try to avoid oil from entering the heat exchange system.
② Discharge the air in a timely manner: Air in the condenser will increase the condensing temperature. When the air pressure in the system reaches 0.2MPa, the power consumption will increase by 18%, and the cooling capacity will drop by 8%. Therefore, every effort should be made to prevent air from infiltrating into the system and discharge the infiltrated air in a timely manner.
③ Regularly remove scale and clean the circulating water tank: Keep the condensed water clean. When the condenser is scaled by 1.

5mm, the power consumption will increase by 9.7%.
④ Defrost in a timely manner: After the surface of the evaporator is frosted, it will lead to deteriorated heat transfer, a drop in the evaporation temperature, and an increase in power consumption.
⑤ Utilize the low temperature at night in summer to cool down: When the temperature difference between day and night in the summer and autumn seasons in the local area reaches more than 10°C, reasonably utilize the low temperature at night, and the energy-saving effect is obvious.
(4) Correctly estimate the changes in the actual cooling consumption of the cold storage. Master the heat release during the food processing process, the changes in the outside air temperature, the cooling water temperature, the heat during daily operations, and other patterns of changes in the cooling consumption. Keep good daily management records and adjust the number of compressors turned on at any time to make the cooling production of the turned-on compressors adapt to or be close to the actual cooling consumption of the cold storage.
(5) On the premise of ensuring that the cooling load is met, try to reduce the number of compressors turned on and improve the operation efficiency of the compressors. Choose to turn on 1 compressor with a large cooling capacity instead of 2 compressors with a small cooling capacity; choose to turn on a single-unit two-stage compressor instead of 2 combined two-stage compressors.
(6) Adjust the startup time. On the premise of not affecting the cold storage quality of food, reduce the running time of the refrigeration compressors during the day (it is best to turn them on at noon), and increase the running time of the refrigeration compressors at night, that is, choose to start them during the low-power-consumption period (that is, turn them on late at night); not only can the cost be reduced, but also the condensing temperature at night is relatively low, which can reduce the power consumption of the compressors.
II. Reducing the Cooling Loss of the Insulated Storage Rooms in the Cold Storage
(1) Ensure the thermal insulation performance of the enclosure structure of the cold storage. Having a good enclosure structure of the cold storage is a prerequisite for ensuring the low-temperature environment inside the cold storage. When designing a new cold storage, thermal insulation materials with a small thermal conductivity coefficient should be used for the enclosure structure, and pay attention to the integrity of the enclosure structure. Try to avoid the generation of cold bridges and through-wall holes, reduce the heat transfer from the outside of the cold storage to the inside, and further reduce the cooling load loss of the enclosure structure of the cold storage.
(2) Reasonable startup control and appropriate evaporation temperature
① The refrigeration compressor is the most power-consuming equipment in the cold storage. In the design of the cold storage, the compressor configuration is generally determined according to the maximum mechanical load conditions that occur throughout the year to meet the requirements of the peak heat load period. However, in actual operation, due to the changes in the peak and off-peak seasons of food cold processing and storage, the changes in the daily and night air temperatures throughout the year, and other changing factors, the full-load running time of the compressor selected during the design is often short, and the low-load running time is long. Therefore, the compressor operates under conditions less than the designed load for most of the running time, and there is great potential for energy saving. At present, most cold storages still use manual operation to adjust the startup, and the phenomenon of blind startup is widespread. On the premise of ensuring the quality of the stored food, having an appropriate cold storage temperature in the cold storage is also an indicator reflecting the energy saving of the system. Because an appropriate cold storage temperature can reduce the temperature difference inside and outside the cold storage, which is conducive to reducing the cooling load and the power load of the refrigeration system.
② When producing the same amount of cooling capacity, increasing the evaporation temperature can reduce the power consumption of the compressor. Because when the condensing temperature remains unchanged, increasing the evaporation temperature will correspondingly increase the suction pressure of the compressor, reduce the specific volume of the suction steam, increase the cooling capacity per unit volume, reduce the compression ratio, increase the volumetric efficiency, and reduce the energy consumption when producing the same amount of cooling capacity.

For example, for the compressor, when the evaporation temperature increases by 1°C each time, the cooling production per kilowatt-hour will increase by about 2.4%, and the energy-saving effect is remarkable. During daily operation, the corresponding reasonable storage temperature should be determined according to the requirements of different varieties, qualities, and storage periods of cold-stored food.
Appropriately increasing the evaporation temperature can not only reduce the heat transfer temperature difference, reduce the dry consumption of food, and improve product quality, but also increase the cooling capacity per unit shaft power of the compressor. Avoid the occurrence of an increase in the condensing temperature.
When the suction temperature of the compressor remains constant, an increase in the condensing temperature leads to a decrease in the cooling capacity per unit volume, an increase in the compression ratio, a decrease in the volumetric efficiency, and an increase in energy consumption when producing the same amount of cooling. For example, for every 1°C decrease in the condensing temperature, the cooling capacity per unit shaft power will increase by about 2.6%. Therefore, maintaining a lower condensing temperature is beneficial for reducing the power consumption of the compressor.
(3) Timely and regular defrosting
During the operation of the air cooler, as the frost layer gradually thickens, the heat transfer coefficient decreases, the air volume decreases, the fan power increases, and the cooling capacity of the air cooler drops sharply. Therefore, the air cooler must be defrosted after operating for a certain period of time. Currently, in large and medium - sized cold storages in China using ammonia as the working medium, most designs adopt a defrosting method that combines water and hot ammonia. However, in actual operation, for the sake of convenience and to reduce operating procedures, the single water - flushing defrosting method is more commonly used.
Although water - flushing defrosting is simple and easy to implement, it has many deficiencies:
① High energy consumption and rapid temperature rise in the cold storage. Water - flushing defrosting requires additional power consumption for the water pump. During defrosting, a large amount of heat is added to the cold storage, and the temperature in the cold storage rises rapidly. Generally, it takes 1 - 2 hours to cool down to the temperature before defrosting after defrosting.
② It cannot solve the problem of oil accumulation in the evaporator.
③ If water overflows or splashes on the ground during defrosting, it will damage the thermal insulation layer of the floor.
④ The defrosting time is relatively long.
Therefore, it is recommended to use the hot - ammonia defrosting method as much as possible. In the hot - ammonia defrosting method, since the heating for defrosting expands from the inside to the outside, it has little impact on the temperature in the cold storage, and the temperature drops quickly after defrosting, avoiding the deficiencies of water - flushing defrosting, which is worthy of promotion. However, an electric heater should be added to the water - receiving tray of the air cooler to prevent the melted frost water from refreezing and blocking the sewer. In addition, the cold - storage door should be avoided being opened during defrosting.
(4) Reducing the cold air loss at the cold - storage door
The cold - storage door should be opened and closed immediately to reduce the load loss when opening the door. For example, if the opening time of the cold - storage door is doubled, the cold loss will increase several times. At the same time, if the cold - storage door is open for a long time, high - humidity air outside the cold storage will invade, and frost and dew will easily form at the door opening, thereby damaging the structure of the cold - storage body. The best way to ensure the immediate opening and closing of the cold - storage door is to use an automatic control structure. If the door is open for too long, the cold - storage door will automatically close to achieve energy - saving effects. The area of the cold - storage door, especially its height, has a significant impact on cold loss.
Research shows that for cold air leakage, the height of the cold - storage door has a much greater impact than its width. Therefore, its height should be reduced as much as possible. The power of the electric heating wire of the cold - storage door has two options: anti - dew and anti - freezing. The configured power of the electric heating wire for cold - storage doors at different operating temperatures varies. Selecting an appropriate heating power can save 2% of energy. To reduce the energy loss and structural damage caused by the door opening, a vestibule or an air curtain can be set at the door opening to reduce the invasion of high - temperature and high - humidity air outside the cold storage, reduce the cooling load, and improve the system efficiency.
(5) Lighting control inside the cold storage
According to the regulations in the Cold Storage Refrigeration Design Manual, the lighting in the cold - storage room should be 1.8 - 5.8 W/m². However, in actual projects, due to usage requirements, it often exceeds this regulation, and in some cases, it even reaches about 10 W/m². If the lights are forgotten to be turned off, it not only wastes lighting electricity but also increases the heat load of the cold - storage room and the refrigeration system. Therefore, adding simple automatic control can avoid lighting waste. If the lighting switch is not turned off 5 - 15 minutes after the cold - storage door is closed, the lighting can be automatically turned off. The lighting delay time should exceed the time of a single operation by workers inside to avoid accidentally turning off the lights in the cold storage. If the lights are accidentally turned off, they can be turned on with the help of the long - burning lights in the cold - storage room and the safety settings of the cold - storage door to ensure the operational safety of the staff.
(6) Using mechanized operations
When loading, unloading, and handling food, a large number of workers often enter the cold storage, which can easily cause a sudden increase in the heat load inside the cold storage, resulting in a larger temperature fluctuation inside the cold storage, reducing the storage effect, and increasing the cooling load of the refrigeration system, which is extremely unfavorable for the energy - saving work of the system. Therefore, using mechanized operations can avoid a large number of workers entering the cold storage for operations at the same time, thereby achieving energy - saving effects for the system.
(7) Using a closed platform for loading and unloading
Using a closed low - temperature platform can not only ensure the quality of frozen food to the maximum extent but also significantly reduce the heat load entering the cold storage from the outside due to the temperature difference. It can also greatly reduce the moisture entering the low - temperature space, reduce the defrosting frequency, and improve the refrigeration efficiency of the system. However, cold storages using a closed platform will increase the corresponding civil engineering costs and the difficulty of loading and unloading.
III. Automatic control system for energy saving in cold storages
(1) Automatic control for energy saving in cold storages
The automatic control for energy saving in cold storages involves the programming of energy - saving control procedures and the selection of automatic control components. Manufacturers of automatic control components, professional design institutes, or capable users can all undertake the research and development of automatic control for energy saving in cold storages. However, considering the practicality and efficiency of the control system, the automatic control for energy saving in cold storages is best jointly developed by manufacturers and design institutes (with manufacturers taking the lead and design institutes providing support), and continuously improved during the implementation process by the users, and new automatic control products are continuously developed.
(2) Specific design and application of automatic control for energy saving in cold storages
The implementation process of automatic control for energy saving in cold storages usually involves design, installation and commissioning, trial operation, performance evaluation and correction until it meets the design requirements and achieves the energy - saving goal. When the content of the project changes, it can be modified at any time to meet the requirements of the cold - storage users. Energy saving in cold storages often needs to be achieved through advanced refrigeration equipment, appropriate system matching, flexible response measures, and strict operation management. This requires refrigeration technicians to be familiar with energy - saving requirements and combine the characteristics of the project on the basis of optimizing the refrigeration process design to design a complete automatic control process for energy saving in cold storages. Electrical automatic control technicians complete the electrical automatic control design according to the automatic control process and use professional knowledge to simplify and optimize the automatic control process.
Energy saving in cold storages is an important part of the automatic control of cold storages. The automatic control of cold storages consists of two parts: refrigeration and electricity. Only through the joint efforts of all technicians can the automatic control of cold storages be effective and the energy - saving goals of cold storages be achieved. The trial operation of the automatic control for energy saving in cold storages is also a very important part. During the trial operation, close contact should be maintained with the users and professional manufacturers. Analyze the operation effect with the users and discuss correction measures with the professional manufacturers. In the daily operation and management of cold storages, people are the most important factor.
Improving the management level from the above aspects to achieve energy - saving operation of cold storages can achieve good economic benefits.